A two-stroke cycle engine is an internal combustion engine that completes a cycle of operation with a single complete rotation of a crankshaft and two strokes of a piston connected to the crankshaft. The strokes are typically denoted as compression and power strokes. One example of a two-stroke cycle engine is an opposed-piston engine in which two pistons are disposed in the bore of a cylinder for reciprocating movement in opposing directions along the central axis of the cylinder. Each piston moves between a bottom dead center (BDC) location where it is nearest one end of the cylinder and a top dead center (TDC) location where it is furthest from the one end. The cylinder has ports formed in the cylinder sidewall near respective BDC piston locations. Each of the opposed pistons controls one of the ports, opening the port as it moves to its BDC location, and closing the port as it moves from BDC toward its TDC location. One of the ports serves to admit charge air into the bore, the other provides passage for the products of combustion out of the bore; these are respectively termed “intake” and “exhaust” ports (in some descriptions, intake ports are referred to as “air” ports or “scavenge” ports). In a uniflow-scavenged opposed-piston engine, pressurized charge air enters a cylinder through its intake port as exhaust gas flows out of its exhaust port, thus gas flows through the cylinder in a single direction (“uniflow”) along the length of the cylinder, from intake port to exhaust port.
Charge air and exhaust products flow through the cylinder via an air handling system (also called a “gas exchange” system). Fuel is delivered by injection from a fuel delivery system. As the engine cycles, a control mechanization governs combustion by operating the air handling and fuel delivery systems in response to engine operating conditions. The air handling system may be equipped with an exhaust gas recirculation (“EGR”) system to reduce production of undesirable compounds during combustion.
In an opposed-piston engine, the air handling system moves fresh air into and transports combustion gases (exhaust) out of the engine, which requires pumping work. The pumping work may be done by a gas-turbine driven pump, such as a compressor (e.g., a turbocharger), and/or by a mechanically-driven pump, such as a supercharger. In some instances, the compressor unit of a turbocharger may be located upstream or downstream of a supercharger in a two-stage pumping configuration. The pumping arrangement (single stage, two-stage, or otherwise) can drive the scavenging process, which is critical to ensuring effective combustion, increasing the engine's indicated thermal efficiency, and extending the lives of engine components such as pistons, rings, and cylinders. Additionally, pressure and suction waves in the intake and exhaust can also provide pumping work. The pumping work also drives an exhaust gas recirculation system.
Opposed-piston engines have included various constructions designed to transport engine gasses (charge air, exhaust) into and out of the cylinders. For example, U.S. Pat. No. 1,517,634 describes an early opposed-piston aircraft engine that made use of a multi-pipe exhaust manifold having a pipe in communication with the exhaust area of each cylinder that merged with the pipes of the other cylinders into one exhaust pipe. The manifold was mounted to one side of the engine.
In the 1930s, the Jumo 205 family of opposed-piston aircraft engines defined a basic air handling architecture for dual-crankshaft opposed-piston engines. The Jumo engine included an inline cylinder block with six cylinders. The construction of the cylinder block included individual compartments for exhaust and intake ports. Manifolds and conduits constructed to serve the individualized ports were attached to or formed on the cylinder block. Thus, the engine was equipped with multi-pipe exhaust manifolds that bolted to opposite sides of the engine so as to place a respective pair of opposing pipes in communication with the annular exhaust area of each cylinder. The output pipe of each exhaust manifold was connected to a respective one of two entries to a turbine. The engine was also equipped with intake conduits located on opposing sides of the engine that channeled charge air to the individual intake areas of the cylinders. A two-stage pressure charging system provided pressurized charge air for the intake conduits.
The prior art exhaust manifolds extracted a penalty in increased engine size and weight. Each individual pipe required structural support in order to closely couple the pipe opening with the annular exhaust space of a cylinder. Typically, the support was in the form of a flange at the end of each pipe with an area sufficient to receive threaded fasteners for sealably fastening the flange to a corresponding area on a side of the cylinder block. The flanges of each manifold were arranged row-wise in order to match the inline arrangement of the cylinders. The width of the ducts connected to these flanges restricted cylinder-to-cylinder spacing, which required the engine to be comparatively heavy and large.